The power reserve indicator of a timepiece mechanism or movement becomes complicated when several energy accumulators are arranged to deliver their energy to the mechanism or to the movement.
In particular, in order to obtain an increased power reserve, several accumulators can be arranged in series, notably barrels. It is possible to view the overall power reserve by using a differential mechanism, including one input per accumulator or barrel. For example, in the case of two barrels mounted in series, the power reserve indication requires a first input for the first barrel (winding) and a second input on the second barrel (letting down). This differential mechanism with separate inputs occupies a large volume within the timepiece movement, which often makes it impossible to provide a timepiece with both, on the one hand, several accumulators and a differential display, and on the other hand, other complications.
EP Patent No 1582943 in the name of RICHEMONT discloses a timepiece movement provided with at least three barrels all housed between a base plate and a bar, said base plate and the bar configured to carry two superposed barrels, and the third barrel being placed laterally with respect to the first two, without superposition, the toothing of the third barrel meshing with that of the other two barrels.
CH Patent Application No 694411A5 in the name of PARMIGIANI discloses a power reserve indicator device including a star wheel held in position by a jumper and integral with a display means, for watches with a double barrel, having manual winding or self-winding. A first winding barrel includes a winding pin actuating a winding lever driving the star wheel in a first direction of rotation, and a second letting-down barrel which includes a letting-down pin actuating a letting-down lever driving the star wheel in a second direction opposite to the first.